The Extinction Curve in the Visible and the Value of Rv. Part II: Addendum to AN 333, 160

Abstract

This paper corrects and completes a previous study of the shape of the extinction curve in the visible and the value of Rv. A continuous visible/infrared extinction law proportional to 1/λ^p with p close to 1 ({\pm}0.4) is indistinguishable from a perfectly linear law (p = 1) in the visible within observational precision, but the shape of the curve in the infrared can be substantially modified. Values of p slightly larger than 1 would account for the increase of extinction (compared to the p = 1 law) reported for λ > 1μm and deeply affect the value of Rv. In the absence of gray extinction Rv must be 4.04 if p = 1. It becomes 3.14 for p = 1.25, 3.00 for p = 1.30, and 2.76 for p = 1.40. Values of p near 1.3 are also attributed to extinction by atmospheric aerosols, which indicates that both phenomena may be governed by similar particle size distributions. A power extinction law may harmonize visible and infrared data into a single, continuous, and universal, interstellar extinction law.

This article does not replace but completes arXiv:1109.2199 (A.N. 333, 160). Accepted for publication (Apr 26, 2012). To appear in Astron. Nachr. (July, 2012)